1. Field of the Invention
This invention relates to a method and apparatus for feeding fuel to heat engines, in particular to internal combustion engines which operate on hydrogen.
2. Description of the Prior Art
The problems of atmospheric pollution, and more recently the energy crisis, have given increasing importance to research into overcoming the problems by the use of hydrogen as a fuel. In fact, it has been known for a long time that hydrogen can be used as a fuel, and, in the field of pollution, it constitutes the fuel producing the smallest discharge of pollutants, such as carbon monoxide and hydrocarbons. The exhaust gases from hydrogen combustion consist exclusively of water vapor apart from oxides of nitrogen which can easily be eliminated. Furthermore, hydrogen has a very high calorific value (29 kcal/kg). On the other hand, the increased net cost of hydrogen and its low volumetric weight in the gaseous form have hitherto prevented hydrogen from being extensively used as a fuel, especially in motor vehicles.
On the other hand, it is known to store hydrogen in the form of metal hydrides in the solid state, particularly magnesium hydride which delivers 70g of gaseous hydrogen per kg of hydride. Magnesium hydride, which is stable at ordinary temperatures, liberates its hydrogen content around 240.degree. C at pressures which increase with temperature. The hydride can be regenerated by hydrogenation under pressure, the hydrogenation proceeding the more readily the more finely divided is the powder of base metal.
The known devices for producing hydrogen from metal hydrides in a motor vehicle consist essentially of a tank in which the hydride is heated. Such devices have the disadvantage of a large thermal inertia which, on the one hand, makes the vehicle extremely slow to start up and, on the other hand, makes the hydrogen production continue for a certain time after heating has ceased when the engine of the vehicle is stopped. The arrangement therefore completely lacks the requisite flexibility for commercial acceptance. A further difficulty arises in that if the hydrogen is injected directly into the combustion chambers of the engine the hydrogen pressure must constantly be sufficient. The high thermal inertia of the known arrangements makes it practically impossible to adjust the hydrogen pressure by control of the heating power.